Sphinx: TypeError: '_traversal_list' object is not reversible

[lpsinger]

Describe the bug
I get the following error when building my documentation set:

Exception occurred:
  File "/src/.eggs/Sphinx-2.2.2-py3.7.egg/sphinx/util/nodes.py", line 151, in apply_source_workaround
    for classifier in reversed(node.parent.traverse(nodes.classifier)):
TypeError: '_traversal_list' object is not reversible
The full traceback has been saved in /tmp/sphinx-err-5sxhweij.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!

For the full output, see the attached file sphinx-err-5sxhweij.log.

To Reproduce
Steps to reproduce the behavior:

$ docker run --rm -it python bash
# git clone https://git.ligo.org/emfollow/gwcelery
# cd gwcelery
# python setup.py build_sphinx

Expected behavior
The documentation for my project builds successfully.

Your project
http://git.ligo.org/emfollow/gwcelery/

Environment info

• OS: Debian 10.2
• Python version: 3.8.0
• Sphinx version: 2.2.2
• Sphinx extensions: celery.contrib.sphinx, matplotlib.sphinxext.plot_directive, sphinx.ext.autodoc, sphinx.ext.autosectionlabel, sphinx.ext.extlinks, sphinx.ext.graphviz, sphinx.ext.intersphinx, sphinx.ext.napoleon, sphinx.ext.viewcode

[lpsinger]

Looks like this broke with docutils==0.16b0.

[aowen87]

We're also seeing this when building VisIt docs. Is there a workaround or patch that we can apply for the time being? We build with sphinx 2.2.1 and are getting the following error while building our docs:

Exception occurred:
  File "/Users/maguire7/Desktop/VisIt_repo/libs_dev/third_party/python/3.7.5/i386-apple-darwin18_clang/lib/python3.7/site-packages/Sphinx-2.2.1-py3.7.egg/sphinx/util/nodes.py", line 151, in apply_source_workaround
    for classifier in reversed(node.parent.traverse(nodes.classifier)):
TypeError: '_traversal_list' object is not reversible

[matham]

I had the same issue. The workaround is to not use the latest beta release of docutils on pypi when installing sphinx. Specifically, I had something like pip install --pre sphinx, changing to pip install sphinx resolved the issue because the latest stable version of docutils does not have the problem.

Hopefully it will be fixed before docutils makes a new stable release.

[aowen87]

We altered a section of our config file to use a lower version of docutils, and this seemed to work for us.

[tk0miya]

Thank you for reporting. It seems docutils adds some incompatible changes to new beta release. I'll try to fix it later.

[tk0miya]

Fixed by #6918
Thank you for reporting!

[williamdes]

Would that explain https://salsa.debian.org/phpmyadmin-team/phpmyadmin/-/jobs/505908#L1141 ?

[tk0miya]

@williamdes It seems you are using Sphinx-1.8.5 and docutils-0.16, right? This has been fixed in Sphinx-2.3.0. If so, please update Sphinx to latest one or pin docutils to 0.15 or older.

FYI: We only supports latest version of Sphinx. So my recommendation is updating Sphinx.

[williamdes]

Well https://packages.debian.org/sid/docutils-common has "0.15.2+dfsg-2" in Debian and https://packages.debian.org/source/sid/sphinx is at "1.8.5-4"
Unless somebody updates the packages it looks like I will be waiting and having a failed CI

[tk0miya]

_traversal_list was added since docutils-0.16. So it seems the CI execution uses non-debian's docutils.

[williamdes]

Get: 32 http://deb.debian.org/debian sid/main amd64 docutils-common all 0.16~rc1+dfsg-1 [128 kB]

https://tracker.debian.org/pkg/python-docutils explains why that appeared recently.
0.16 is in unstable and the CI uses unstable

Should I open a bug so that a new version is uploaded ?

[tk0miya]

All I can do is please update Sphinx to latest one as you do for docutils. I don't know rule of Debian. But if updating is called a bug in Debian, please open a bug.

[tk0miya]

ping @mitya57 . Could you check this please?

[mitya57]

This fixes it:
https://tracker.debian.org/news/1093549/accepted-sphinx-185-5-source-into-unstable/

[tk0miya]

@mitya57 Thank you for quick work! I really appreciate you :-)